There is known from JP, A No. 8-20257 a drive transmission assembly for working vehicles in which a first fluid-operated speed change mechanism and a second fluid-operated speed change mechanism are arranged within a vehicle body in series in a longitudinal direction of the vehicle body and are connected in series with each other. The first fluid-operated speed change mechanism is operable to perform a speed change transmission between a first drive shaft and a first driven shaft, which are arranged in parallel with each other, by a selective actuation of plural fluid-actuated clutches, whereas the second fluid-operated speed change mechanism is operable to perform a speed change transmission between a second drive shaft and a second driven shaft by a selective actuation of plural fluid-actuated clutches. In the drive transmission assembly disclosed in the above-referenced publication, a direction-reversing mechanism, operable between a primary shaft and an output shaft, is further arranged at a location in front of the first fluid-operated speed change mechanism and is connected thereto in series.
When first and second fluid-operated speed change mechanisms, each of which is operable by a selective actuation of plural fluid-actuated clutches, are provided such that they are connected in series with each other, a speed change transmission of multi-ratios corresponding to the product of change ratios of the first and second speed change mechanisms can be achieved easily because the actuation of fluid-actuated clutches is readily controlled by control valve means.
In the direction-reversing mechanism employed in the transmission assembly disclosed in the above-referenced publication, the output shaft is arranged co-axially with the primary shaft, on which a forward directional fluid-actuated clutch and a backward directional fluid-actuated clutch are mounted, and a counter shaft extending in parallel with the primary shaft is provided at a level below the primary shaft. The output shaft is driven to rotate in the forward running direction of vehicle when the forward directional fluid-actuated clutch is actuated to connect the output shaft directly to the primary shaft, whereas the output shaft is driven to rotate in the backward running direction of vehicle when the backward directional fluid-actuated clutch is actuated to transmit power from the primary shaft to the output shaft through the counter shaft via backward directional gearing. The first drive shaft of first fluid-operated speed change mechanism is integral with the output shaft of a high level, and the first fluid-operated speed change mechanism is structured such that it is operable to perform a speed change transmission between the first drive shaft and the first driven shaft of a low level by a selective actuation of the fluid-actuated clutches which are mounted on the first drive shaft. The second fluid-operated speed change mechanism includes the second drive shaft which is an extension of the first driven shaft of a low level, the driven shaft which is arranged co-axially with the second drive shaft, and a counter shaft which is arranged co-axially with the first drive shaft. The second fluid-operated speed change mechanism is structured such that it provides a high change ratio when a fluid-actuated clutch mounted on the second driven shaft is actuated to connect this driven shaft directly to the second drive shaft whereas it provides a low change ratio when another fluid-actuated clutch mounted on the second driven shaft is actuated to transmit power from the second drive shaft to the second driven shaft through the counter shaft via speed-reduction gearing.
In the above referenced drive transmission assembly disclosed in JP, A No. 8-20257, the plural fluid-actuated clutches of first fluid-operated speed change mechanism are mounted on the first drive shaft of a high level so that the level of an upper surface of the vehicle body is hightened, at a location where these clutches are arranged, because of the large outer size of clutch cylinders of the fluid-actuated clutches. Because first and second fluid-operated speed change mechanisms are usually arranged within the vehicle body at a location in front of a seat for an operator as viewed in a longitudinal direction of the vehicle body, the above referenced arrangement of fluid-actuated clutches hightens the level of an upper surface of the vehicle body at a location around the legs of the operator so that so-called "leg space" is narrowed and the operator has a hardship. Further, although the first and second fluid-operated speed change mechanisms are arranged in series in a longitudinal direction of the vehicle, respective fluid-actuated clutches of these change mechanisms are mounted on the first drive shaft of a high level and on the second driven shaft of a low level so that it is difficult to concentratedly arrange the valve means for the first and second fluid-operated speed change mechanisms or it is required to employ lengthy fluid piping if concentrated arrangement of the valve means is employed. Furthermore, the fluid-actuated clutches of first fluid-operated speed change mechanism, which are arranged at a high level, are not immersed in oil stored within the vehicle body so that these clutches are insufficiently cooled.
Accordingly, a primary object of the present invention is to provide a novel drive transmission assembly for working vehicles in which all the fluid-actuated clutches of first and second fluid-operated speed change mechanisms are mounted on the transmission shafts of low levels so that the level of an upper surface of the vehicle body is kept low, cooling of these clutches is sufficiently attained, and the valve means for these fluid-actuated clutches can be concentratedly arranged.
An attendant object of the invention is to provide an improved drive transmission assembly in which a direction-reversing mechanism is provided in a reasonable manner for achieving the above referenced primary object.
Another attendant object is to provide an improved drive transmission assembly which can easily be assembled.